(1) Field of the Invention
The present invention relates to working fluid compositions for compression type refrigerators, which compositions are each composed of a specific refrigerant and a specific lubricant. More particularly, the invention relates to working fluid compositions for compression type refrigerators, which compositions are each composed of a refrigerant containing no chlorine, such as ammonia or a hydrofluorocarbon, and a lubricant containing a benzotriazole derivative to improve lubricating characteristic.
(2) Related Art Statement
Heretofore, naphthenic mineral oils, paraffinic mineral oils, alkylbenzolic synthesized oils and poly-.alpha.-olefinic synthetic oils are known as lubricants for refrigerators. Such oils are used for the purpose of reducing friction and wear and preventing seizing in sliding sections in compressors.
The refrigeration lubricants have different requirements from those of the ordinary lubricants in that since the former contact a refrigerant, the lubricant must have excellent stability to the refrigerant and excellent solubility with the refrigerant.
With respect to refrigerants containing chlorine, such as dichlorodifluoromethane (R12) conventionally used as a refrigerant, mineral oils such as naphthenic mineral oils, and paraffinic mineral oils, alkylbenzene or poly-.alpha.-olefine have been used. However, environmental problems are pointed out that the refrigerants containing chlorine, such as R12, break the ozone layer and impose serious and bad effects upon the environment. As new refrigerants substituting those refrigerants, hydrofluorocarbons (hereinafter abbreviated as "HFC"s) containing no chlorine, such as 1,1,1,2-tetrafluoroethane (R134a) have been proposed. However, naphthenic mineral oils, paraffinic mineral oils, alkylbenzoic synthesized oils, poly-.alpha.-olefinic oils or the like heretofore used do not dissolve into HFCs such as R134a, and thus they cannot be used therefor.
In order to solve the above problem, Japanese patent application Laid-open No. 1-259,093 etc. proposed to use polyoxyalkylene glycol-based synthetic oils, and Japanese patent application Laid-open No. 3-128,991 etc. proposed to use ester-based synthetic oils. These synthetic oils are well dissolved into R134a, which solves the above-mentioned problem.
However, since extreme-pressure effect (improvement on lubricity) of intramolecular chlorine atoms cannot be expected in the case of the HFC refrigerant containing no chlorine, such as R134a, lubrication becomes poor at a bearing, a piston, a sealing device, etc. of a refrigerator. Consequently, energy is lost, wear becomes greater, or seizing is provoked, or decomposition or degradation of the refrigerant or the lubricant is promoted to cause corrosion. Therefore, high lubricity is required for the refrigeration lubricants composed of such synthetic oils.
Further, phosphorus compounds and sulfur compounds conventionally used, such as tricresil phosphate or dialkyl sulfide, have smaller lubricity-improving effect, and poor solubility with R134a. Further, these compounds exhibit severe corrosiveness against metallic materials such as copper alloys. Wear is a big problem in refrigerators having severe use conditions. Particularly, since wear is likely to occur in the case of refrigerators for car air conditioners, etc. using an aluminum alloy or a copper alloy in a sliding part, strong demand has existed to reduce wear.
On the other hand, it is known that since benzotriazole and benzotriazole derivatives are adsorbed onto the surface of a metal and protect the sliding surface, benzotriazole and the benzotriazole derivatives are used as a corrosion-preventing agent, a metal-deactivator or antioxidant, in a variety of lubricants. Further, Japanese patent application Laid-open No. 2-102,296, EP-A-501440, etc. disclose that lubricants in which benzotriazole or a benzotriazole derivative is blended together with a non-chlorine type refrigerant such as R134a are used in refrigeration oils. In these publications, it is described that benzotriazole or a benzotriazole derivative thereof is used as an antioxidant, or a metal-inactivating agent, or is used to protect the surface of a metal due to corrosion with a carboxylic acid or prevent a copper-plating phenomenon. However, these publications are utterly silent about improvement upon wear resistance.
Japanese patent application Laid-open No. 2-102,296 describes that metal-deactivator such as benzotriazole and benzotriazole derivatives may be used as an antioxidant, and benzotriazole and benzotriazole derivatives are recited therein as antioxidants together with phenol-based, amine-based or phosphorus-based antioxidants. However, with respect to benzotriazole and benzotriazole derivatives, a wear resistance-improving effect is not disclosed at all. In addition, this publication does not disclose at all what chemical structures the benzotriazole derivatives have.
EP501440 describes refrigerator oils in which benzotriazole or a benzotriazole derivative is blended as an additive into a special ester-based synthetic oil together with a phosphorus-based anti-wear agent, an epoxy compound and a chelate-based metal-deactivator. However, benzotriazole derivatives are used for the purpose of protecting the surface against corrosion of a metal with a carboxylic acid or preventing copper-plating. Therefore, the addition amount of the benzotriazole or the benzotriazole derivative is low. This reference does not refer to an anti-wear effect of the benzotriazole derivative.
Benzotriazole described in Japanese patent application Laid-open No. 2-102,296 and EP-A-501440 is a compound expressed by the following formula, which has been used in various lubricants. It is well known that benzotriazole is effective for the prevention of oxidation and corrosion, but this benzotriazole has completely no wear-preventing effect. ##STR2##